I am planning to attach a 6V 100mA Solar Panel to a Step Up USB Charger you can see at this link, and yes I know it can only be charged during the day... that is OK.

Considering that most phone batteries today are at least 2000 mAh, would connecting two solar panels in parallel speed up the charging? In other words, does amperage of input into the booster have a direct correlation to the output amps, or would it be inefficient?


I updated the link to a different product that can give up to 2A of output current and takes up to 5.5V input. I plan to connect the two solar panels in parallel to the Step Up USB module. I will connect one end of a regular USB to the step up module and the other to the phone.

I realise that I am wasting power when I am not charging my phone. Perhaps I'll do that in my next DIY.

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    \$\begingroup\$ "Considering that most phone batteries today are at least 2000 mA": not "mA", mAh, which is an entirely different unit. The current that a battery can provide is not the same as the capacity of the battery. \$\endgroup\$
    – uint128_t
    Feb 12, 2017 at 16:46
  • \$\begingroup\$ That's right. I read it's best not to charge a battery at more than 10% of its capacity. So I implied that I could double my charge (to 200 mA) when my battery is 2000 mAh. NP? \$\endgroup\$ Feb 12, 2017 at 17:03

1 Answer 1


Yes, certainly. The output power will always be less than the input power, but specifically it will be a portion of the input power determined based on the converter efficiency (which is claimed to be 96% for that device). So connecting two cells in parallel would allow approximately double the output current (assuming the converter can handle the current and doesn't limit it).

But that converter steps up to 5V. If you are supplying 6V to it, the output may be up to 6V. Also, that is not a charger, it is only a boost converter. You shouldn't connect it directly to a battery.

  • \$\begingroup\$ My understanding is that it will give 6V at the brightest sun, and in reality it'd be more like 5.2V actual, based on a review. Lower light should yield lesser, right? The booster has a 600 mA output limit, so what I want to do is a good plan, right? The solar will be connected to the booster, my charging USB cable goes into the booster's female pin, and the other end into my phone. \$\endgroup\$ Feb 12, 2017 at 17:08

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